SPARKS STREET, CAMBRIDGE:
ONE OR TWO INNOVATIONS TOO MANY

"Hmm, the shopping list says that I need some Worcestershire sauce,
and some lettuce, and cake mix." But all in all, traffic engineering is unlike going
shopping for groceries:

A recent traffic-calming installation on Sparks Street in Cambridge is
more like an attempt to prepare a dinner from these ingredients: "oh no, the
Worcestershire sauce makes a poor frosting for the cake, and a poor dressing for the
salad. Darn, I can't make anything at all from this!

Sparks Street between Brattle Street and Mt. Auburn Street in Cambridge is
one-way, and passes through a residential neighborhood. The City of Cambridge has
installed curb extensions (bulbouts) so that parking shifts from one side of the street to
the other at the end of each block. The purpose of shifting the lane position is evidently
to slow motorists by preventing them from driving straight. Note the parking lane on
the left in the foreground in the photo below, and on the right in the background.

A parallel-parked motorist can more easily get in and out when the
driver's seat is on the curb side. But when exiting the parking space, and more
importantly, the motorist can more easily see and yield to overtaking traffic if the
driver's seat is on the street side -- as is usual on two-way streets.

The City has installed a bike lane on Sparks Street, always on the right
side. Two vehicles shown in the photo are continuing straight in the bike lane rather than
slowing down and jogging over to the left. More than a dozen vehicles passed me as I took
the photos on this page. All of them drove in the bike lane.

The traffic law requires drivers to merge to the right curb before turning. However,
as the photo below shows, a solid white bike lane line extends up to the crosswalk before
the intersection, and the bike lane has dashed borders only inside the intersection,
directing motorists to turn right from the left lane. The bike lane also directs
bicyclists to swerve left. A knowledgeable bicyclist would merge left before the
intersection in order to establish right of way and avoid conflict with right-turning
motorists. Now, that would slow overtaking motorists. But the premise of traffic
calming is to constrict vehicle movement in order to slow traffic -- rather than to allow
the normal interaction of vehicles on the road to slow the traffic.

How might motorists
be made to jog left? A barrier between the bike lane and the rest of the street would
accomplish that, but it would constrain bicyclists to enter the bike lane in the door zone
after the intersection, and would interfere with turning movements by large vehicles.

Bicyclist directed to swerve across path of right-turning
motor traffic.
Photos taken April 14, 2005